Ocean circulation around the Antarctic coastal margins plays a critical role in heat delivery to Antarctica, melting ice shelves. However, until recently, satellite-based sea-level observations have been limited by the presence of sea ice. With improved algorithms, it is now possible to monitor sea-level fluctuations over most of the Southern Ocean, including sea ice-covered areas. We identified several clockwise gyres along East Antarctic coastal margins in satellite-derived dynamic ocean topography (DOT). Singular value decomposition analyses revealed that the coastal DOT deepening and anomalous clockwise circulation consistently occur during the positive phase of the southern annular mode (SAM), which is associated with negative wind stress curl anomalies. Shifting of the SAM to a more positive phase since the 20th century and its expected continuation into the coming century could lead to enhanced clockwise gyres along East Antarctica, contributing to increased poleward ocean heat transport.

To clarify the impact of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a, and stable oxygen isotopic ratios (δ18O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Off the TIS, modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf and flowed along bathymetric troughs into the TIS cavity, where it met the ice shelf base and formed a buoyant mixture with glacial meltwater. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, DIC, TA, and nutrient concentrations on the surface of the ice front were decreased by photosynthesis and the dilution effect of meltwater from sea ice and the base of the ice shelf. The partial pressure of CO2 (pCO2) in surface water was reduced by photosynthesis and dilution, and the surface water became a strong CO2 sink for the atmosphere. The DIC and TA (normalized to salinity of 34.3 to correct for dilution effects) changed in a molar ratio of 106:16 because of phytoplankton photosynthesis. The decrease of pCO2 by more than 100 μatm with respect to mCDW was thus the result of photosynthesis. The nutrient consumption ratio suggested that enough iron was present in the water column to supply the surface layer via buoyancy-driven upwelling and basal melting of the TIS.